Crystal structure of human bleomycin hydrolase, a self-compartmentalizing cysteine protease

Background: Bleomycin hydrolase (BH) is a cysteine protease that is found i n all tissues in mammals as well as in many other eukaryotes and prokaryote s. Although its conserved cellular function is as yet unknown, human bleomy cin hydrolase (hBH) has clinical significance in that it is thought to be t he major cause of tumor cell resistance to bleomycin chemotherapy. In addit ion, it has been reported that an allelic variant of hBH is genetically lin ked to Alzheimer's disease. Results: We have determined the crystal structures of wild-type hBH and of a mutant form of the enzyme. The overall structure is very similar to that of the previously determined yeast homolog, however, there is a striking di fference in the charge distribution. The central channel, which has a stron g positive electrostatic potential in the yeast protein, is slightly negati ve in hBH. We have determined that hBH does not have the DNA-binding activi ty of the yeast protein and that the enzyme is localized to the cytoplasm. Conclusions: The difference in charge distribution between the yeast and hu man BH enzymes is most likely responsible for the difference in DNA-binding activity. Nevertheless, the C-terminal autoprocessing activity and the rol e of the C terminus as a determinant for peptidase activity are conserved b etween the yeast and human forms. The structure of hBH suggests that the pu tative Alzheimer's disease linked variation does not directly alter the int rinsic peptidase activity. Rather, the position of the mutation suggests th at it could affect interactions with another protein, which may modulate pe ptidase activity through repositioning of the C terminus.